1. Field of the Invention
The present invention relates to a video rendering apparatus and method and a program for the rendering of videos.
2. Description of the Related Art
In computer graphics (CG) rendering, a technique called global illumination is used. Global illumination is a technique for performing illumination calculation in rendering an object in a scene in consideration of the influences of indirect light from other objects around the target object.
Conventional illumination calculation cannot reproduce an effect produced when light reflected by an object illuminates another object, and hence is performed considering that uniform light called ambient light illuminates portions to which light is not directly applied. In contrast to this, global illumination can express a reflection effect and light-gathering effect similar to those in the real world, and hence allows more realistic rendering of videos.
Indirect light calculation techniques in global illumination include several types, e.g., radiosity, photonmap, and path tracing. All these techniques are based on intersection determination of lines of sight (rays) passing through pixels of an image and an object. Basically, therefore, the calculation time is proportional to the resolution of an image.
For this reason, attempts have been made to shorten the calculation time and interactively render a global illumination video by performing intersection determination only at low-resolution sampling points placed at proper intervals, instead of performing intersection determination of rays and an object with respect to all the pixels of an image, and increasing the resolution of the resultant data by filtering afterward.
In these attempts, some contrivance is made to, for example, concentrate sampling points at positions which greatly differ from each other in terms of time, instead of placing sampling points at equal intervals, or change the tap positions for filtering (which indicate specific points to be filtered) so as to prevent the contour lines of an object from blurring (see, for example, K. Bala, B. Walter, and D. P. Greenberg, “Combining Edges and Points for Interactive High-Quality Rendering”, SIGGRAPH2003).
On the other hand, in the field of study on computer vision, studies have been made to reconstruct high-resolution moving images from low-resolution moving images. These studies are roughly classified into two categories including one that uses only the image of one frame and the other that uses the images of a plurality of frames. The former is not very high in reconstruction accuracy because of a limitation on the amount of information obtained, but allows relatively stable calculation. In contrast, the latter is high in theoretical reconstruction accuracy because of the use of the information of a plurality of frames, but needs to calculate matching between a plurality of frames at the subpixel level, which is difficult to stably perform (see, for example, Sung Cheol Park, Min Kyu Park, and Moon Gi Kang, “Super-Resolution Image Reconstruction: A Technical Overview”, IEEE SIGNAL PROCESSING MAGAZINE, May 2003).
As described above, the conventional video rendering apparatus is designed to shorten the calculation time by performing intersection determination of rays and an object only at low-resolution sampling points in rendering a global illumination video, and increasing the resolution of the resultant data by filtering them.
However, since only sampling points in one frame are used for calculation for an increase in resolution, the number of sampling points per frame must be relatively large in order to improve the quality of a high-resolution video. That is, it is difficult to satisfy both the requirements of a shorter calculation time and higher quality.
On the other hand, in the field of computer vision, a resolution increasing technique using a plurality of frames has been studied. This technique may be applied to the calculation of global illumination. However, it is impossible to stably calculate subpixel matching between a plurality of frames, which is required for the above application.
If the pattern (texture) of an object is homogeneous, or the luminance of the object changes with time, a matching error often occurs. In Sung Cheol Park et. al. described above, there is described a technique for reducing the influence of a matching error by performing iterative calculation based on a statistical error model. However, this technique requires a large amount of calculation, and hence is not very suitable for interactive applications.